Vanadium(V) oxide
Precursor to vanadium alloys and industrial catalyst
From Wikipedia, the free encyclopedia
Vanadium(V) oxide (vanadia) is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a dark yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, being the principal precursor to alloys of vanadium and is a widely used industrial catalyst.[8]
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| Names | |
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| IUPAC name
Divanadium pentaoxide | |
| Other names
Vanadium pentoxide Vanadic anhydride Divanadium pentoxide | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.013.855 |
| EC Number |
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| KEGG | |
PubChem CID |
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| RTECS number |
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| UNII | |
| UN number | 2862 |
CompTox Dashboard (EPA) |
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| Properties[1] | |
| V2O5 | |
| Molar mass | 181.8800 g/mol |
| Appearance | Yellow solid |
| Density | 3.35 g/cm3[2] |
| Melting point | 681 °C (1,258 °F; 954 K)[2] |
| Boiling point | 1,750 °C (3,180 °F; 2,020 K)[2] (decomposes) |
| 0.7 g/L (20 °C)[2] | |
| +128.0×10−6 cm3/mol[3] | |
| Structure[4] | |
| Orthorhombic | |
| Pmmn, No. 59 | |
a = 1151 pm, b = 355.9 pm, c = 437.1 pm | |
| Distorted trigonal bipyramidal (V) | |
| Thermochemistry[5] | |
Heat capacity (C) |
127.7 J/(mol·K) |
Std molar entropy (S⦵298) |
131.0 J/(mol·K) |
Std enthalpy of formation (ΔfH⦵298) |
−1550.6 kJ/mol |
Gibbs free energy (ΔfG⦵) |
−1419.5 kJ/mol |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H302, H332, H335, H341, H361, H372, H411 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
10 mg/kg (rat, oral) 23 mg/kg (mouse, oral)[6] |
LCLo (lowest published) |
500 mg/m3 (cat, 23 min) 70 mg/m3 (rat, 2 hr)[6] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) |
C 0.5 mg V2O5/m3 (resp) (solid)[7]
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| Safety data sheet (SDS) | ICSC 0596 |
| Related compounds | |
Other anions |
Vanadium oxytrichloride |
Other cations |
Niobium(V) oxide Tantalum(V) oxide |
| Vanadium(II) oxide Vanadium(III) oxide Vanadium(IV) oxide | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The mineral form of this compound, shcherbinaite, is extremely rare, almost always found among fumaroles. A mineral trihydrate, V2O5·3H2O, is also known under the name of navajoite.
Chemical properties
Reduction to lower oxides
Upon heating a mixture of vanadium(V) oxide and vanadium(III) oxide, comproportionation occurs to give vanadium(IV) oxide, as a deep-blue solid:[9]
- V2O5 + V2O3 → 4 VO2
The reduction can also be effected by oxalic acid, carbon monoxide, and sulfur dioxide. Further reduction using hydrogen or excess CO can lead to complex mixtures of oxides such as V4O7 and V5O9 before black V2O3 is reached.
Acid-base reactions
V2O5 is an amphoteric oxide, and unlike most transition metal oxides, it is slightly water soluble, giving a pale yellow, acidic solution. Thus V2O5 reacts with strong non-reducing acids to form solutions containing the pale yellow salts containing dioxovanadium(V) centers:
- V2O5 + 2 HNO3 → 2 VO2(NO3) + H2O
It also reacts with strong alkali to form polyoxovanadates, which have a complex structure that depends on pH.[10] If excess aqueous sodium hydroxide is used, the product is a colourless salt, sodium orthovanadate, Na3VO4. If acid is slowly added to a solution of Na3VO4, the colour gradually deepens through orange to red before brown hydrated V2O5 precipitates around pH 2. These solutions contain mainly the ions HVO2−4 and V2O4−7 between pH 9 and pH 13, but below pH 9 more exotic species such as V4O4−12 and HV10O5−28 (decavanadate) predominate.
Upon treatment with thionyl chloride, it converts to the volatile liquid vanadium oxychloride, VOCl3:[11]
- V2O5 + 3 SOCl2 → 2 VOCl3 + 3 SO2
Other redox reactions
Hydrochloric acid and hydrobromic acid are oxidised to the corresponding halogen, e.g.,
- V2O5 + 6 HCl + 7 H2O → 2 [VO(H2O)5]2+ + 4 Cl− + Cl2
Vanadates or vanadyl compounds in acid solution are reduced by zinc amalgam through the colourful pathway:
The ions are all hydrated to varying degrees.
Preparation
Technical grade V2O5 is produced as a black powder used for the production of vanadium metal and ferrovanadium.[10] A vanadium ore or vanadium-rich residue is treated with sodium carbonate and an ammonium salt to produce sodium metavanadate, NaVO3. This material is then acidified to pH 2–3 using H2SO4 to yield a precipitate of "red cake" (see above). The red cake is then melted at 690 °C to produce the crude V2O5.
Vanadium(V) oxide is produced when vanadium metal is heated with excess oxygen, but this product is contaminated with other, lower oxides. A more satisfactory laboratory preparation involves the decomposition of ammonium metavanadate at 500–550 °C:[13]
- 2 NH4VO3 → V2O5 + 2 NH3 + H2O
Uses
Ferrovanadium production
In terms of quantity, the dominant use for vanadium(V) oxide is in the production of ferrovanadium (see above). The oxide is heated with scrap iron and ferrosilicon, with lime added to form a calcium silicate slag. Aluminium may also be used, producing the iron-vanadium alloy along with alumina as a byproduct.
Sulfuric acid production
Vanadium(V) oxide is used as the oxygen-transfer catalyst in the contact process, the only process now used for the industrial production of sulfuric acid.[14] The catalyst phase is a molten salt formed from vanadium(V) oxide and added alkali metal sulfates acting as co-catalysts. In this melt, the reactive complex [(VO)2O(SO4)4]4−, which is regarded as the actual catalytic species, is formed. Oxygen and sulfur dioxide coordinate to this complex and react to form sulfur trioxide without a change in the oxidation state of vanadium.[14]
- The overall reaction is:
- 2 SO2 + O2 ⇌ 2 SO3
The reaction is carried out at about 420 to 620 °C; at lower temperatures the catalyst is deactivated by formation of vanadium(IV) compounds, while at higher temperatures it begins to decompose.[14] Industrial conversion is performed in multi-bed contact furnaces, in which the catalyst is arranged in four superposed layers and the process gas is cooled between the beds to maintain the required temperature range.
Other oxidations
Maleic anhydride is produced by the V2O5-catalysed oxidation of butane with air:
- C4H10 + 4 O2 → C2H2(CO)2O + 8 H2O
Maleic anhydride is used for the production of polyester resins and alkyd resins.[16]
Phthalic anhydride is produced similarly by V2O5-catalysed oxidation of ortho-xylene or naphthalene at 350–400 °C. The equation for the vanadium oxide-catalysed oxidation of o-xylene to phthalic anhydride:
- C6H4(CH3)2 + 3 O2 → C6H4(CO)2O + 3 H2O
The equation for the vanadium oxide-catalysed oxidation of naphthalene to phthalic anhydride:[17]
- C10H8 + 4+1⁄2 O2 → C6H4(CO)2O + 2 CO2 + 2 H2O
Phthalic anhydride is a precursor to plasticisers, used for conferring pliability to polymers.
A variety of other industrial compounds are produced similarly, including adipic acid, acrylic acid, oxalic acid, and anthraquinone.[8]
Other applications
Due to its high coefficient of thermal resistance, vanadium(V) oxide finds use as a detector material in bolometers and microbolometer arrays for thermal imaging. It also finds application as an ethanol sensor in ppm levels (up to 0.1 ppm).
Vanadium redox batteries are a type of flow battery used for energy storage, including large power facilities such as wind farms.[18] Vanadium oxide is also used as a cathode in lithium-ion batteries.[19]
Vanadium pentoxide is often used as a component in glazes where it produces a wide range of colours from greens and yellows to blues and grays.[20]
Biological activity
Vanadium(V) oxide exhibits very modest acute toxicity to humans, with an LD50 of about 470 mg/kg. The greater hazard is with inhalation of the dust, where the LD50 ranges from 4–11 mg/kg for a 14-day exposure.[8] Vanadate (VO3−4), formed by hydrolysis of V2O5 at high pH, appears to inhibit enzymes that process phosphate (PO3−4). However the mode of action remains elusive.[10][better source needed]
